The present invention relates to molybdated dispersants suitable for use as lubricant additives, and a method for their preparation.
Current engine lubrication technology requires ever-improving performance of the lubricant in order to assure adequate lubrication of demanding engines. It is known that the presence of molybdenum compounds can in many instances provide improvements in anti-wear performance and, in particular, friction reduction and, as a consequence, fuel economy. However, many molybdenum compounds are expensive or difficult to provide in a suitably oil-soluble form.
Canadian Patent 623,155, Jul. 4, 1961, discloses lubricant additives containing molybdenum compounds. Phosphomolybdic acid is reacted with an organic nitrogen base and reduced by reaction with an organic compound to a form in which at least a part of the Mo is tetravalent. The resulting product has improved solubility. Suitable nitrogen bases include (in the claims) hydrocarbon acyl amines. All known organic nitrogen bases that are soluble in or at least compatible with liquid lubricants are said to be suitable for use in neutralizing and reducing phosphomolybdic acid and for neutralizing and enhancing the thermal stability of an acidic reaction product of phosphomolybdic acid with a non-basic reducing agent. The final reaction products are said to be useful as lubricant additives.
U.S. Pat. No. 5,319,119, Kaneshima et al., Jun. 7, 1994, discloses oleophilic molybdenum compounds comprising an aliphatic amine group and a heteropolyanion group. The oleophilic molybdenum compound is a catalyst precursor capable of being changed to a catalyst having excellent catalytic activity. The catalyst can be prepared by reacting an aliphatic amine with a heteropolyacid in a hydrocarbon oil. Lubricating oil is disclosed as an illustrative hydrocarbon oil.
The present invention, therefore, solves the problem of improving lubricant performance, particularly in terms of friction reduction, in an economical manner by providing oil-soluble molybdenum compositions which can be prepared by a convenient route.
The present invention provides a molybdated dispersant composition prepared by reacting phosphoric acid or silicic acid, MoO3, and an amine-containing dispersant. Otherwise stated, it provides a molybdated dispersant composition represented by the formula:
(R1xe2x80x94NR2R3H+)mxe2x88x92nXn(MoHPA)mxe2x88x92
wherein R1xe2x80x94NR2R3 represents the amine-containing dispersant, R1 is a group providing dispersant properties to said dispersant composition, each of R2 and R3 is independently hydrogen, a hydrocarbyl group, or an additional R1 group; X is hydrogen, a monovalent metal ion, a single valence of a polyvalent metal ion, an ammonium ion, or an amine cation, m is 3 or 4, n is 0 to 2.5 when m is 3 and 0 to 3.5 when m is 4, and (MoHPA)mxe2x88x92 is a molybdenum heteropolyacid anion of charge m.
The invention similarly provides a process for preparing a molybdated composition comprising reacting phosphoric acid or silicic acid with MoO3 and with an amine, such as an amine-containing dispersant.
The invention further provides a lubricant composition comprising a major amount of an oil of lubricating viscosity and such a molybdated dispersant, or a concentrate thereof.
Various preferred features and embodiments will be described below by way of non-limiting illustration.
The present invention provides a molybdated dispersant composition. It is believed that the molybdated dispersant has, at least in part, a composition or structure which can be reasonably represented by the formula:
(R1xe2x80x94NR2R3H+)mxe2x88x92nXn(MoHPA)mxe2x88x92
In this formula, R1xe2x80x94NR2R3 represents an amine-containing dispersant in which R1 is a group providing dispersant properties to said dispersant composition. That is, R1, or a portion of R1, is a group which provides sufficient solubility properties to the molybdenum-containing composition set forth above so that it can be readily dispersed or dissolved in oil. Thus, the entire moiety R1xe2x80x94NR2R3 can be considered to be a dispersant, and it generally comprises a relatively less polar R1 group, together with a generally more polar NR2R3 portion, both groups together serving to provide the dispersant properties. The more polar portion, or head, serves to interact with polar substances, which ordinarily would be dirt or contaminant particles; but for the purposes of the present invention, it interacts with the molybdenum heteropolyacid. The less polar portion provides oil solubility to permit the compound or complex to be dissolved or dispersed in oil. It is possible that an R1 group also contains additional amine groups, which may be considered to be a part of the polar xe2x80x9cheadxe2x80x9d of the dispersant, provided that at least a portion of an R1 group is a suitably non-polar moiety. Indeed, some of the additional amine groups which may be present in R1 may form additional salt structures or otherwise interact with additional molybdenum heteropolyacids to form more complicated structures such as:
(MoHPA)mxe2x88x92Xn(+HR2R3Nxe2x80x94R4xe2x80x94NR2R3H+)Xn(MoHPA)mxe2x88x92
(ignoring for the purpose of illustration the stoichiometry of the structure) where R4 is a linking group such as a straight chain or branched alkylene group, and the other terms are as described below.
In the formula (R1xe2x80x94NR2R3H+)mxe2x88x92nXn(MoHPA)mxe2x88x92, each of R2 and R3 is independently hydrogen, a hydrocarbyl group, or an additional R1 group as defined above. That is, R2 or R3 may also provide dispersant properties to the complex.
Amine-containing dispersants in general can include acylated amines, amine-containing carboxylic esters, Mannich reaction products, hydrocarbyl substituted amines, and mixtures thereof.
Acylated amine dispersants include reaction products of one or more carboxylic acylating agent and one or more amine. The carboxylic acylating agents include C8-30 fatty acids, C14-20 isoaliphatic acids, and hydrocarbyl substituted carboxylic acylating agents. Dimer acids are described in U.S. Pat. Nos. 2,482,760, 2,482,761, 2,731,481, 2,793,219, 2,964,545, 2,978,468, 3,157,681, and 3,256,304. The addition carboxylic acylating agents are addition (4+2 and 2+2) products of an unsaturated fatty acid with one or more unsaturated carboxylic reagents. These acids are taught in U.S. Pat. No. No. 2,444,328. In another embodiment, the carboxylic acylating agent is a hydrocarbyl substituted carboxylic acylating agent. The hydrocarbyl substituted carboxylic acylating agents are prepared by a reaction of one or more of olefins or polyalkenes with one or more of unsaturated carboxylic agents, such as itaconic, citraconic, or maleic acylating agents, typically at a temperature of 160xc2x0, or 185xc2x0 C. up to 240xc2x0 C., or to 210xc2x0 C. Maleic acylating agents are the preferred unsaturated acylating agent. The procedures for preparing the acylating agents are. well known to those skilled in the art and have been described for example in U.S. Pat. No. 3,412,111; and Ben et al., xe2x80x9cThe Ene Reaction of Maleic Anhydride With Alkenesxe2x80x9d, J. C. S. Perkin II (1977), pages 535-537. A preferred acylating agent is a hydrocarbyl-substituted succinic anhydride or the reactive equivalent thereof (e.g., an acid, acid halide, half ester). The hydrocarbyl substituent thereon is, in a preferred embodiment, a polymer of isobutylene having a number average molecular weight of 500 to 5000, preferably 900 to 3500.
The amines which react with the acylating agents may be known amines, and in the present instance a polyamine, such that at least one amine functionality can remain unacylated and available for reaction to form the molybdated dispersant of the present invention. Polyamines include aliphatic, cycloaliphatic, heterocyclic or aromatic polyamines and alkylene polyamines, condensed polyamines, hydroxy containing polyamines, arylpolyamines, and heterocyclic polyamines.
Alkylene polyamines are represented by the formula 
wherein n has an average value from 1 or 2 to 10, or to 7, or to 5, and the xe2x80x9cAlkylenexe2x80x9d group has from 1 or 2 to 10, or to 6, or to 4 carbon atoms. Each R is independently hydrogen, or an aliphatic or hydroxy-substituted aliphatic group of up to 30 carbon atoms. Acylated amines, their intermediates and methods for preparing the same are described in U.S. Pat. Nos. 3,219,666; 4,234,435; 4,952,328; 4,938,881; 4,957,649; 4,904,401; and 5,053,152.
In a preferred embodiment, the relative amounts of the amine and of the hydrocarbyl-substituted succinic anhydride which are reacted are such that the mole ratio of carbonyl groups to nitrogen atoms in the resulting succinimide dispersant is about 0.4:1 to 1.5:1, and preferably 0.7:1 to 1.4:1.
In another embodiment, the dispersant can be a carboxylic ester, provided that it also contains an amino group. The carboxylic ester is prepared by reacting one or more carboxylic acylating agents, preferably a hydrocarbyl substituted carboxylic acylating agent, with at least one organic hydroxy compound and optionally an amine. The hydroxy compound may be an alcohol (if an amine is also used) or a hydroxy containing amine.
The alcohols may contain non-hydrocarbon substituents of a type which do not interfere with the reaction of the alcohols with the acid (or other acylating agent) to form the ester. In one embodiment, the alcohols can be polyhydric alcohols, such as alkylene polyols.
Carboxylic ester dispersants may be prepared by any of several known methods. A preferred method involves the reaction of the carboxylic acylating agents described above with one or more alcohol or phenol in ratios 0.5 equivalent to 4 equivalents of hydroxy compound per equivalent of acylating agent, as described in U.S. Pat. Nos. 3,522,179 and 4,234,435. The carboxylic ester dispersants may be further reacted with at least one amine such as those described above, in order to provide the required amine functionality. Suitable amines include polyethylenepolyamines, condensed polyamines (i.e., acid catalyzed condensation products of amine reactants with hydroxy alkyl or hydroxy aryl reactants as taught in U.S. Pat. No. 5,053,152), or heterocyclic amines, such as aminopropylmopholine. The amine can be added in an amount sufficient to react with any non-esterified carboxyl groups, while retaining amine functionality to react with the molybdenum heteropolyacid. In one embodiment, the carboxylic ester dispersants are prepared by reacting from 1 to 2 equivalents, or from 1.0 to 1.8 equivalents of hydroxy compounds, and up to 0.3 equivalent, or from 0.02 to 0.25 equivalent of polyamine per equivalent of acylating agent. The carboxylic acid acylating agent may be reacted simultaneously with both the hydroxy compound and the amine. There is generally at least 0.01 equivalent of the alcohol and at least 0.01 equivalent of the amine although the total amount of equivalents of the combination should be at least 0.5 equivalent per equivalent of acylating agent. These carboxylic ester dispersant compositions are known in the art, and the preparation of a number of these derivatives is described in, for example, U.S. Pat. Nos. 3,957,854 and 4,234,435.
In another embodiment, the dispersant may simply be a hydrocarbyl-substituted amine. Hydrocarbyl-substituted amines are well known to those skilled in the art. These amines and methods for their preparation are disclosed in U.S. Pat. Nos. 3,275,554; 3,438,757; 3,454,555; 3,565,804; 3,755,433; and 3,822,289. Typically, hydrocarbyl substituted amines are prepared by reacting olefins and olefin polymers, including the above polyalkenes and halogenated derivatives thereof, with amines (mono- or polyamines). The amines may be any of the amines described above, preferably an alkylenepolyamine. Examples of hydrocarbyl substituted amines include ethylenepolyamines such as diethylene-triamine; poly(propylene)amine; N,N-dimethyl-N-poly(ethylene/propylene)-amine, (50:50 mole ratio of monomers); polybutene amine; N,N-di(hydroxy-ethyl) -N-polybutene amine; N-(2-hydroxypropyl)-N-polybutene amine; N-poly-butene -aniline; N-polybutenemorpholine; N-poly(butene)ethylenediamine; N-poly (propylene)trimethylenediamine; N-poly(butene)diethylenetriamine; Nxe2x80x2,Nxe2x80x2-poly (butene)tetraethylenepentamine; and N,N-dimethyl-Nxe2x80x2-poly(propylene)-1,3-propylenediamine. Similar molybdated compositions can be prepared by the reaction (described in greater detail below), of phosphoric or silicic acid, MoO3, and an amine, even if the amine is not specifically a dispersant.
In another embodiment, the dispersant can be a Mannich dispersant. Mannich dispersants are generally formed by the reaction of at least one aldehyde, such as formaldehyde and paraformaldehyde, at least one of the above described amines, preferably a polyamine, such as a polyalkylenepolyamine, and at least one alkyl substituted hydroxyaromatic compound. The amounts of the reagents is such that the molar ratio of hydroxyaromatic compound to formaldehyde to amine is in the range from (1:1:1) to (1:3:3). The hydroxyaromatic compound is generally an alkyl substituted hydroxyaromatic compound. This term includes the above described phenols. The hydroxyaromatic compounds are those substituted with at least one, and preferably not more than two, aliphatic or alicyclic groups having from 6 to 400, or from 30 to 300, or from 50 to 200 carbon atoms. These groups may be derived from one or more of the above described olefins or polyalkenes. In one embodiment, the hydroxyaromatic compound is a phenol substituted with an aliphatic or alicyclic hydrocarbon-based group having an {overscore (M)}n of 420 to 10,000. Mannich dispersants are described in the following patents. U.S. Pat. Nos. 3,980,569; 3,877,899; and 4,454,059.
Dispersants can also be treated by or reacted with a variety of agents to produce well-known variants. Such agent include sulfurizing agents such as elemental sulfur or CS2 and dimercaptothiadizoles. Reactions of dispersants with a dimercaptothiadiazole is taught, for example, in U.S. Patent No. 4,136,043.
In the formulas given above, the heteropolyacid anion (MoHPA)mxe2x88x92is not necessarily completely neutralized by the amine-containing dispersant. This fact is represented by the optional presence in the formula of X, which can be hydrogen, a monovalent metal ion, a single valence of a polyvalent metal ion, an ammonium ion, or an amine cation from a source other than a dispersant, or mixtures of the above. The amount of X present in a given structure is that amount which, together with the ion from the dispersant, is sufficient to satisfy the valence or charge of the molybdenum heteropolyacid. The valence of the heteropolyacid, represented by m, is typically 3 or 4: 3 when it is a phosphorus based material and 4 when it is a silica based material. The amount of X, represented by n, is typically 0 to 2.5 when m is 3 and 0 to 3.5 when m is 4. Preferably X is hydrogen. In a preferred embodiment, n is zero, that is, there is substantially no X in the composition.
Molybdenum containing heteropolyacids and their corresponding anions, represented herein by (MoHPA)mxe2x88x92, are well known materials. Heteropolyanions are polymeric oxoanions formed by a condensation reaction of two or more different oxoanions, e.g.,
12MoO42xe2x88x92+HPO42xe2x88x92+23 H+xe2x86x92(PMo12O40)3xe2x88x92+12H2O
Formation of the corresponding heteropoly acid is simply the reaction:
12MoO3+H3PO4xe2x86x92H3PMO12O40.
A similar reaction can be written with silicic acid:
12MoO3+H4SiO4xe2x86x92H4SiMo12O40
forming silicomolybdic acid, the anion of which can have a charge of 4xe2x88x92.
A variety of structures are known for these materials; they can have, for instance, the so-called Keggin structure, wherein twelve MoO6 octahedra surround a central PO4 tetrahedron (in the case where phosphorus is employed). Other structures and related formulas are also known, including PMo,12O406xe2x88x92, PMo18O626xe2x88x92, P2Mo5O234xe2x88x92, PMo9O349xe2x88x92, P2Mo18O62 6xe2x88x92, PMo11O397xe2x88x92, PMo9W3O403xe2x88x92, GeMo12O404xe2x88x92, SiMo3W9O405xe2x88x92, and TeMo6O246xe2x88x92, where P, Ge, Si, or Te and Mo or W are taken as representative elements and the indicated structure is an ion with the appropriate charge. The central atom of the Keggin structure, which is typically phosphorus, as shown, can also be any of the Group IIIA to Group VIIA (ACS numbering) metalloids or non-transition metals, including P, As, Si, Ge, B, Al, Sb, and Te. The molybdenum (Mo) in the above formula fills the role known as the xe2x80x9cpoly atom,xe2x80x9d which can in general be any of the Group VB or VIB transition metals, including W, V, Cr, Nb, Mo, or Ta, although of course for the present invention molybdenum is desired. Thus suitable materials include preferably phosphomolybdates and silicomolybdates. Other combinations selected from among the above elements are also possible, including arsenomolybdates, teluromolbydates, and aluminomolybdates, and phosphovanadylmolybdates, the latter representing a mixed material having a formula (for the anion portion) of PV2Mo10O405xe2x88x92. The preferred material is a phosphomolybdate, which term generally encompasses both the acid and the various salts, described below. The preferred species of the (MoHPA)3is PMoI12O 403xe2x88x92.
For more detailed information on the structures of heteropolyacid materials, attention is directed to Chemical Reviews, January/February 1998, Vol. 98 (No. 1) and Misono, xe2x80x9cHeterogeneous Catalysis by Heteropoly Compounds of Molybdenum and Tungsten,xe2x80x9d Catal. Rev.-Sci. Eng., 29(2and3), 269-321 (1987), in particular, pages 270-27 and 278-280. In the present invention, the hydrogen ions have been partially or fully replaced by a dispersant anion, R1xe2x80x94NR2R3H+ as described above, that is, the heteropolyacid is a partially or fully neutralized salt of the heteropolyacid.
Heteropoly acids are commercially available materials, (e.g., Aldrich Chemical Company, #22,420-0 and 38,336-8). The salts are similarly commercially available. Alternatively, they can be prepared from the acid materials by neutralization with an appropriate amount of base. Heteropoly acids are generally received in a hydrated form. They can be employed in this form (uncalcined) or they can be treated (calcined) to remove some or all of the water of hydration, that is, to provide a dehydrated or otherwise modified species.
It is difficult or impossible to determine precisely the structural form in which the molybdated dispersants of the present invention exist. It is believed that the molybdenum atoms in the composition of the present invention predominantly or entirely retain the +6 oxidation state. While it is believed that at least a portion, and probably a substantial portion, of the molybdated dispersants exhibit the heteropoly acid type structures as set forth above, this has not been unambiguously determined. The present invention is therefore intended to encompass other related structures that may be formed. Accordingly, the molybdated dispersants are also described by their various methods of preparation.
One way by which the molybdated dispersants of the present invention can be prepared is by mixing an amine-containing dispersant with a molybdenum heteropolyacid (or a partially neutralized salt thereof) and permitting the neutralization reaction to occur to form the desired salt. Since many dispersants are commercially available as a solution with 40-60% diluent oil, the diluent oil can provide a convenient medium in which the reaction is run. For efficient reaction, it is preferred that the molybdenum heteropolyacid be supplied to the reaction mixture as a solution of preferably 10-50% by weight (more preferably 20-30% by weight) of the heteropolyacid in a lower alkanol, that is, containing up to 3 or 4 carbon atoms, such as ethanol or, preferably, methanol. The alcohol preferably contains no more than a minor amount of water.